Abstract

The superconductivity of , , , and is intercompared. The stretched -lattice parameter of in comparison to and decides empirically the population of their and bands and as a result their transition temperature values, respectively, at 39 and 9.5 K for the first two and no superconductivity for the later. The nonstoichiometry induces an increase in parameter with Boron excess both in and . Magnetization and resistivity measurements in case of niobiumboride samples show the absence of superconductivity in stoichiometric sample while a clear diamagnetic signal and a transition for boron excess samples. On the other hand, superconductivity is not achieved in case. The probable reason behind is the comparatively lesser or insufficient stretching of parameter.